Abstract: Journal of Material Sciences & Applied Engineering

Abstract:
Using the light year as a unit of measurement helps to determine the age of the celestial bodies. When an object is observed from the earth one light year away, this means that we see it as it was a year ago, because according to the definition of the light year, it is the amount of light that the light travels in a year, i.e. how many It took a while for it to reach us, so when we say the Andromeda galaxy is 2.5 million years away from Earth, that means we're seeing what it was like 2.5 million years ago.